This invention relates to a process for the cracking of crude oil using partial combustion gases wherein superheated steam, crude oil and oxygen are injected into a partial combustion zone at one or more points.
It is known in the prior art that crude oil and other hydrocarbon fractions may be thermally cracked by mixing superheated steam and the oil together and allowing the pyrolysis to proceed adiabatically. See, for example, French Pat. No. 1,577,043 dated Aug. 1, 1969, and S. Araki, et al. "Pyrolysis of Hydrocarbons Using Superheated Steam as Heat Carrier", World Petroleum Congress, Moscow, USSR. (September, 1971). These processes allow crude and heavy hydrocarbon fractions, which would foul conventional tubes, to be cracked and have the advantage that the steam diluent and heat carrier may be readily condensed from the products and a savings is thereby made as only the product gases need to be compressed for separation. Among the disadvantages of these processes are expense associated with the generation of the superheated steam in the 1699.degree. to 2000.degree. C. range generally required. Also among the by-products formed in the cracking process are heavy aromatic liquids and coke which foul reactors and heat exchangers and which contain high quantities of sulfur and metals which must be disposed of. Some of the problems associated with the generation of superheated steam have apparently been solved by using a hydrogen burner to generate high temperature gases, but the yields that may be obtained in this manner are still low and the by-products still remain a problem.
Other process for pyrolysis of heavy hydrocarbons involve the use of a partial or complete combustion burner, where the crude oil or fractions thereof to be cracked is sprayed into the hot gases from the burner. Examples of these are U.S. Pat. Nos. 2,244,636; 2,698,830; 2,912,475; 3,178,488; 3,236,763; 3,408,417; British Pat. No. 1,440,424; and Belgium Pat. No. 838,290. These processes avoid some of the problems associated with the generation of high temperature steam and (when partial combustion is used) also produce hydrogen gas which lowers the heat requried for cracking, increases ethylene yield, and aromatics yield, and reduced coke formation. See, for example, Kunugi, et al. "Pyrolysis of Hydrocarbons in Hydrogenselective Production of Ethylene" World Petroleum Congress (1967).
The main disadvantage of these processes is that large quantities of non-condensable gases (especially carbon monoxide) are produced, which must be compressed to be removed. This involves a considerable cost for large compressors and large size separation equipment.
In U.S. Pat. No. 4,134,824 a process is disclosed in which crude oil is first distilled to separate asphaltic components. The distillate is then cracked using partial combustion gases from a methane burner to generate ethylene with recycling of the asphaltic components to the burner. The main disadvange of this process appears to be the generation of pitch which must be disposed of.